Sex Hormones, the brain and behavior

Definitions of Sex Genetic Gonadal Hormonal Morphological Behavioral (gender role behavior) Identity

Control of Sex Hormones neural inputs Hypothalamus Indirect Loop Short Loop GnRH Adenohypophysis LH, FSH Direct Loop Testes or Ovaries Testosterone or Estrogen & Progesterone Target tissues

Sexual Dimorphisms Phenotypic differences between males and females They can be: anatomical physiological behavioral cognitive They can be: qualitative quantitative

Effects of Sex Hormones Organizational Effects structural sensitive period irreversible masculinization/defeminization Activational Effects act on existing structure no sensitive period reversible

testes differentiate ovaries differentiate

Bipotential tissues: Undifferentiated tissue that can differentiate into either a male or female form. Sexual Dimophisms: Structures, functions or behaviors that differ qualitatively or quantitatively between the sexes.

Prototypical Experiment (Males) Castrate male hamster at birth (before period of brain differentiation) Test in adulthood inject with testosterone place with receptive female male typical behavior low mounting, intromission (ejaculation not possible) inject with estrogen and progesterone place with male female-typical behavior high darting, ear-wiggling, lordosis

Prototypical Experiment (Females) Neuter female hamster at birth and inject with testosterone (before period of brain differentiation) Test in adulthood inject with testosterone place with receptive female male typical behavior high (mounting) inject with estrogen and progesterone place with male female-typical behavior low (ear-wiggling, darting, lordosis)

Kelley, D.B. (1988) Ann. Rev. Neurosci., 11, 225-251.

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Differentiation of the Brain Two processes both are dependent on fetal androgens Masculinization Induction of male characteristics Defeminization Suppression of female characteristics

Estradiol is the sex hormone primarily responsible for masculinization of the brain.

Why aren’t all females masculinized? α-fetoprotein binds to estradiol extracellulary and prevents entry into cell

Steroid Hormones

cholesterol

Control of Sex Hormones neural inputs Hypothalamus Indirect Loop Short Loop GnRH Adenohypophysis LH, FSH Direct Loop Testes or Ovaries Testosterone or Estrogen & Progesterone Target tissues

Control of Stress Hormones neural inputs (limbic system) Hypothalamus Indirect Loop Short Loop CRF (aka CRH) Adenohypophysis Corticotrophin (aka ACTH) Direct Loop Adrenal Cortex Cortisol or Corticosterone Target tissues This is usually referred to as the “HPA axis,” but is now often called the “LHPA axis.”

Suppose there is a deficiency of either estradiol aromatase 5-alpha reductase cholesterol DHT Suppose there is a deficiency of either 21-hydroxylase or 11-β hydroxylase.

cholesterol

estradiol aromatase 5-alpha reductase cholesterol DHT

Testosterone 5-α reductase Dihydrotesosterone

Sex differences in cognition Studies of mathematically gifted Effects of brain damage Anatomical studies of brain laterality Functional (fMRI) studies of brain laterality

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Benbow 20 year follow-up Benbow, C.P., Lubinski, D., Shea, D.L. & Eftekhari-Sanjani, H. (2000) Sex differences in mathematical reasoning ability at age 13: Their status 20 years later. Psychological Science, 11, 474-480.

Brain Laterality

Meta-analysis of data from 13 studies of unilaterally brain-damaged adult humans Females Males Totals Left Positive 15/111 (9%) 100/246 (41%) 115/357 (32)% Right Positive 16/103 (16%) 120/276 (43%) 136/379 (36%) 31/214 (14%) 220/522 (42%) Data from: Inglis, J. & Lawson, J.S. (1981) Sex differences in the effects of unilateral brain damage on intelligence. Science, 212, 693-695.

Cerebral Lateralization Geshwind’s Theory of Cerebral Lateralization Geschwind, N. & Galaburda, A.S. (1987) Cerebral lateralization. Cambridge, MA: MIT Press

McManus, I.C. & Bryden, M.P. (1991) Geschwind’s theory of cerebral lateralization: Developing a formal, causal model. Psych. Bull., 110, 237-253.

Control of Sex Hormones neural inputs Hypothalamus Indirect Loop Short Loop GnRH Adenohypophysis LH, FSH Direct Loop Testes or Ovaries Testosterone or Estrogen & Progesterone Target tissues

Activational Effects of Sex Hormones on Cognition perform well on verbal and motor tasks poorly on spatial tasks perform well on spatial tasks, poorly on motor and verbal tasks

de Lacoste-Utamsing, C. & Holloway, R.L. (1982) Splenium de Lacoste-Utamsing, C. & Holloway, R.L. (1982) Sexual dimorphism in the human corpus callosum. Science, 216, 1431-1432.

Gladue, Green & Hellman (1983) Science, 225, 1496-1499.

Gladue, Green & Hellman (1983) Science, 225, 1496-1499.

LeVay, S. (1991) Science, 253, 1034-1037

Size related to sexual identity not sexual orientation